Irrigation study holds some surprises

A University of Georgia study has looked at the irrigation habits of farmers in drought and rainy conditions for the past five years. And the study shows they can vary widely.

Scientists working on the Agricultural Water Potential Use and Management Program in Georgia, gathered data monthly from about 800 irrigated fields in the state.

They gathered daily, automated data from about 180 of these fields in the Dougherty Plain.

That's where much of Georgia's irrigation takes place, says Jim Hook, a professor with the University of Georgia College of Agricultural and Environmental Sciences.

The initial study began in 1999 and is scheduled to end this month. But the Georgia Environmental Protection Division has asked that it continue another year. EPD funded the study with $250,000 in each of the five years.

“We can compare data taken during four years of drought conditions (from 1999 to 2002) in the state and one year of good rainfall (in 2003),” says Hook, who worked on the study.

Data from the study shows that most Georgia farmers don't apply as much water as previously figured during drought.

They aren't using water to go for the highest possible yields for many crops, either, says Kerry Harrison, a UGA Extension Service irrigation expert who also worked on the study.

In the mid-1990s, the Natural Resources Conservation Service figured Georgia farmers would need to apply 18 acre-inches of water in a dry growing season to give a crop optimal yields (1 acre-inch of water is about 27,000 gallons, or the amount in a typical swimming pool).

But that's not what Georgia farmers do, according to the study.

The 2002 growing season was a severe drought in Georgia. The corn farmers monitored that year in southwest Georgia applied, on average, 13 inches of water to their crop.

“How much water farmers apply can't be tied to one number,” Harrison says. “These are averages. The study tells us that irrigation management styles can vary widely for the same crop.”

The 2003 growing season wasn't a drought year. Corn farmers that year applied, on average, about half the water they did in 2002.

“In the real world, farmers weigh the cost of applying water to how much return they get from increasing yields,” Harrison says. It costs about $4 to apply 1 acre-inch of water.

The study also shows:

Over the five-year study, 30 percent of the monitored sites had vegetables grown on them.

Farmers apply about the same amount of water to vegetable crops like sweet corn, tomatoes and peppers as they do to row crops like peanuts and cotton. But they often have two vegetable crops in one year.

The average age of a Georgia irrigation system is 13 years. But 80 percent of systems in the study have had newer, more efficient water nozzles put on them.

Farmers applied irrigation most often on Thursday. They irrigated the least on Sunday.